Have you ever experienced a moment in your sex life in which sex has become less pleasurable and enjoyable than it used to be? Well, it kind of like you enter a cycle in which your system has become cold in terms of how your body normally responds to sexual stimulation. Therefore, you no longer feel the same passion, drive, energy, and excitement you usually feel while the desire to indulge in is there. I mean you have the desire, but it's not backed up by the same level of passion. It seems like when going through that cycle sex has become quite boring. You kind of feel empty and dissatisfied afterward. That cycle may last up to 2 weeks. Then after that, everything seems to go back to normal. The passion, drive, energy, and so forth have come back. And suddenly, the pleasure that you used to enjoy has come back as well.
That sounds to me you need to change the way you do things. Explore new ideas with your partner and push the boundaries. Sex should never become boring.
The sex you have should not be something that remains static. It should not remain the same as what you learnt in your teens or twenties. The sex should continually evolve, and get better, as you age. The best sex is when you evolve and age with a partner, and try things you can only do with someone you have a long term commitment and trust in. But in order for this to happen you have to be able to communicate, discuss each others needs honestly, and experiment a little. Putting your trust in your partner and seeing where it leads, is a great enabler to a long lasting, frequent, satisfying and varied sex life and intimacy.